Empty section flags

[Fangrui Song]

On 2020-03-03, Fangrui Song wrote:
>On Sun, Feb 9, 2020 at 9:21 PM Alan Modra <amodra@gmail.com> wrote:
>>
>> On Thu, Feb 06, 2020 at 05:25:33PM +0000, bd1976 llvm wrote:
>> > Hi Alan, thanks for the input here. I wonder if it wouldn't be more
>> > consistent to error in all cases - even in the case of different group
>> > signatures. The only exception would need to be for the special section
>> > names (.text, .debug_str, etc...) that the assembler has special knowledge
>> > of (as you explained).
>>
>> Yes, let's see how that goes.
>> https://sourceware.org/ml/binutils/2020-02/msg00129.html
>>
>> > I wonder why creating multiple sections with the
>> > same name for section directives with different group signatures was
>> > implemented - why not just require the use of a distinct section name for
>> > these?
>>
>> I think plain ".text" for a group's text section is fine.  Distict
>> names would just be yet another thing to track for a group.
>>
>> > Or, now that GNU has the ",unique,N" assembly extension (
>> > https://sourceware.org/ml/binutils/2020-02/msg00028.html) that could be
>> > used if the section name is fixed - it would then be explicit in the source
>> > code that another section with the same name will be created.
>>
>> Perhaps, but we aren't designing a new toolchain.  Backwards
>> compatibility can't be discarded without compelling reasons.
>>
>> --
>> Alan Modra
>> Australia Development Lab, IBM
>
>For empty flags, should there be an error as well?
>
>  .section .foo,"ax",@progbits; .byte 1
>  .section .foo,"",@progbits; .byte 2  # no diagnostic
>  .section .foo,"a",@progbits; .byte 3  # Error: changed section
>attributes for .foo
>
>Context: https://github.com/ClangBuiltLinux/linux/issues/913
>
>I lean toward an error for consistency, and I will try making the LLVM
>MC side rule stick.

Thoughts? :)